minor #33878 [Console] Replace posix_isatty with cross-platform, always available stream_isatty (ostrolucky)

This PR was merged into the 5.0-dev branch.

Discussion
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[Console] Replace posix_isatty with cross-platform, always available stream_isatty

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |

stream_isatty is always available since PHP 7.2, which is the minimal version required for Symfony 5.0, so we can remove usages of old, not cross-platform compatible `posix_isatty`

DeprecationErrorHandler left out, since AFAIK it's still meant to be compatible with PHP 5.5

Commits
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c9b8b046a7 Replace posix_isatty with cross-platform, always available stream_isatty

Author: nicolas-grekas

Dumper/CliDumper.php

@@ -587,17 +587,7 @@ private function hasColorSupport($stream): bool
                 || 'xterm' === getenv('TERM');
         }
 
-        if (\function_exists('stream_isatty')) {
-            return @stream_isatty($stream);
-        }
-
-        if (\function_exists('posix_isatty')) {
-            return @posix_isatty($stream);
-        }
-
-        $stat = @fstat($stream);
-        // Check if formatted mode is S_IFCHR
-        return $stat ? 0020000 === ($stat['mode'] & 0170000) : false;
+        return stream_isatty($stream);
     }
 
     /**